All worked examples below use explicitly chosen inputs. They are not measured household averages, utility quotes, or guaranteed savings.
Start with the tariff’s schedule
Some utilities offer time-of-day prices. Peak hours, weekends, seasons, and holidays depend on the plan; there is no nationwide off-peak schedule. Read the current tariff before moving a routine.
Use your utility’s interval usage to total peak and off-peak kWh. A monthly bill total alone does not reveal the split. If only a rough split is available, compare several plausible scenarios.
Compare the entire monthly amount
Take an illustrative 600 kWh month: 180 kWh at 35¢ peak and 420 kWh at 12¢ off-peak, plus a $10 fixed fee. The time-of-use total is $123.40. A flat 20¢ plan with the same $10 fee costs $130.
Move 60 kWh from peak to off-peak without changing total use. The new time-of-use total is $109.60. Shifting saves $13.80 within that plan, and the resulting total is $20.40 below the flat plan. These are invented comparison rates, not a current utility offer.
Find the break-even peak share
With equal fixed fees and the example rates above, the break-even peak fraction is (20 − 12) ÷ (35 − 12), or 34.78%. Below that share, the time-of-use scenario costs less. Above it, the flat plan costs less.
Different fixed charges change this threshold. At low energy use, a larger fixed charge can outweigh a cheaper energy rate. The calculator includes both fees and reports when no break-even point falls between 0% and 100% peak use.
| Peak share | Time-of-use total | Flat total |
|---|---|---|
| 20% | $109.60 | $130.00 |
| 30% | $123.40 | $130.00 |
| 50% | $151.00 | $130.00 |
Check what a two-period comparison leaves out
Tiered rates, demand charges, minimum bills, export credits, and extra seasonal periods need additional tariff calculations. The result is a scenario comparison, not a recommendation to enroll.
Only shift flexible activities in a way that follows the appliance instructions and your household’s needs. A lower bill estimate does not override safety, noise, or comfort constraints.
Sources & calculation notes
References checked 2026-10-09. Example arithmetic is calculated by HomeWattCheck. Article review dates are separate from the EIA data period displayed in our calculators.
Each calculator states its scope beside the result. Appliance tools estimate electricity at one rate; the time-of-use comparator includes two price periods and entered fixed fees. Complex tariffs may need additional calculations. State averages describe reported residential revenue per kWh, not your utility’s offer. See our data sources and methodology or state rate comparison.